Instrument for inspecting the interior of cavities



H. G. BOGART 2,541,976

II-:STRUENT FOR INSPECTING THF.' INTERIOR CF CAVITIES Feb. zo, 1951 2 Sheng-Sheet 1 Filed Nv. 22, 1947 www y.. Nr,

Feb. 20, 1951 H. G. SOGART INSTRUMENT FCR INSPECTING THE '.'NTERIR 0F CAVITIES Filed Nav. 22, 1947 2 Sheets-Shea?. 2

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Q1 www Patented Feb. 2G, 195ib einen INSTRUMENT FOR. INSPECTING THE INTERIOR F CAVITIES Henry G. 'Bagni-t, Brooklyn. N. Y., assigner to Magnailux Corporation, Chicago. lil., a corporation of. Delaware Application November 22, 194'?, Sci-inl No. 787,552

This invention relates to optical instruments intended for use in inspecting the interior of cavities in objects.

In the manufacture of airplane propeller blade.; and similar objects requiring high strength with minimum weight, it has been found that by elimimating the center portions of the structure the weight is materially decreased without a. substantial reduction in strength. However. blades constructed in this fashion have in the past been subject to failure by reasons o! cracks, weld burns and the like on the inside surfaces of the cavity formed by ine holiowed-out central portions. These imperfections have not been detectable for the reason that it has thus for been impossible to conduct a thorough examination of the inteiiorwails oi' the cavity. Moreover, in guns and similar devices it is desirable to inspect the interiors oi cavities to ascertain the presence o! imperfections.

In accordance with the present invention, a lengthy inspecting tube capable of fitting mio the cavity of un airplane propeller, gun, or sniiler device, .is provided with a lamp at one end capable of producing ultraviolet light. A window is formed inthe tube near the lamp to cause illumination ci' the interior of the'cavlty by light therefrom. A retractable filter covers this window and is attached to a rod or wire extending; the length oi the tube, :and which is manipulatab'ie from the end tl'ierec selectively t@ illuminate theV interior of the cavity solely with ultravioletlight or with both ultraviolet light and visible light. A prism, mirror, oroth'er mechenism is placed on the end o? the tubi: to form en image within a relatively smaller optical 'tube extLndingtl-ie length of the main tube and which is in optical cooperation with a suitable viewing device on the end of the :nain tube. Sharp focusing of the imag: of the interior of the cavity relative to the optical system is assured by a resiliently deiiectauie arzi'i extending from the main tube in the rercion nca'r the end thereof and tends the desized focusing. distance relative to the tube. loss or dmtorticn of the image as the tube bends dus toits own weight or to stresses placed upon it, is prevented by' a plurality of lenses placed at intervals along the length thereoi.

Further in accordance with the presen: invention, thev lamp fispose ci the endo the inspecting tube is cooled by a blast of nzrogen or similar inert gas that is incapable of producing ozone under the action c1 ultraviolet light.

This gas ls carried tothe lanipvhy an auxiliary tube disposed within the main inspecting tubeA and which open.; in proximity to tho lamp. 'Ihe heated or spent gas passes through openings provided in the end of the inspecting tube and into the interior oi the cavity being inspected.

To detect weld burns and other visible imperfe'ctlons onv the interior ofthe cavity to be nspected, the apparatus is inserted there-in and the filter shifted to the retracted .position to illuminate the cavity uit-h visible` light. When it is desired to detect crecliis and similar imperfections the cavity is first treated with a fluoressent' substance of thc type that flows into any cracks 'in the cavity and the apparatus is then inserted therein with the filter in the operative position, thus illuminating the interior of the cavity with ultra violet iight and causing fluorescence oiany nii-.ferial held by cracks facing,J the interior of the cavity. i

It is therefore a general object of the present invention to` provide an improved instrument for inspecting the interior oi o cavity.

Another objectl of` the present invention is t0 provide :in improved instrument to inspect the interior of n cavity and which may be. selectively operated to illuminate the cavity with ultraviolet light or visible light.

It is another object of the present .invention io provide iinimproved instrument for inspecting the interior of .s cavity and which contains elements operable from without the cavity seiectively to. illuminate the cavity by either ultraviolet light ci' risible iight.

Still anot'r-er ohect oi the present invention is to provide an improved instrument lor inspect-r ing the interior of a cavityV and which is provided with a novel cooling system which not only prevents overheating thereof but also eliminates any tendency of the instrument to pi'oduce'deterioratngorone gas.

A further object of the present invention is to provide an improve-rl instrument for inspecting the interior o.' a cathy and which is provided with means operable to focus the optical system to assure an image of maximum sharpness.

Vit is yet another object of the present invention to provide en improved instrument for in spcctinii the interior ci :i cavity and which is constructed to avoid distortion 'of images duc to dclections of the instrument.v

Still another object of the present invention is to provide an impr-:ved instrument for inspection of cavities and which Aincludes elements to identily the ocation of n predetermined point on annoio .L the image as seen through the viewing; mechanism,

My invention further resides in features of construction, combination and arrangement whereby an improved .instrument for the inspection of the interior ot a. cavity is provided and which is rugged in construction and reliable in opera.- tion to the end that a unit of maximum utility is achieved.

The nove? features which I believe to be characteristic of. my invention are set. forth with par ticularity in the appended claims. My invention itself, however, both as to its organization and method ci operation, together with further objects and advantages thereof may best be understood 'oy reference to the followingldescription talren in connection with the accompanying drawings.

n the drawings:

Figure l is a side eier-ation view or e. complete mechanism 'constructed in accordance with the principles of the present invention;

Figure .A is a cross soetioxuil view through the axis lA-iA, Figure 1;

Figure 2 is an enlarged end view oi the head portion of the mechanism of' Figure l;

Figure 3 is e. cross Vsectional view through the axis IIL-lll, Figure 2, and showing parts in el vution; K

Figures 4 and 5 are cross sectional views through the axes IV-IV and V-V, Figure 3, respectively;

Figure 6 is a fragmentary top plan View of the heed vportion oi the mechanism of Figure l;

Figure I is o. schematic circuit diagram of an electrical circuit that may be used with the mechanism oi' the present invention;

Figure 8 is a. .fragmentary cross sectional view through the axis WiL-V111, Figure :Zand showing parts in side elevation;

Figure 9' is an enlarged fragmentary side elevational view of the gage structure oi'r the mechanism of Figure l. with parts in cross section; and

Figure l0 is an enlarged fragmentary top plan view of thegage structure oi the mechanism o! Figure l.

is shown on the drawings:

Referring now to Figure i, which is a view showing a completov mechanism constructed ix.-

accordance with ..heprincipes ci the present irivention, the mechanism includes e. lengt-hy inepecting tube T having at one end theheau portion H and at the opposite end the operating portion O.. The head portion H contains a'source ot ultraviolet light, together with the necessary lenses and. a retractable ilter to permit illumination ci the interior oi a cavity having the wall W. The observing or operating port-ion O includes connector elements for attachment to the sources of electrical energy and cooling gas for the elements contained in the head portion and. in addition. includes an eyepiece to observe the image o! the interior of he cavity under inspec tion. The tube T mechanically conn-:cts the head portion and the operating portion and, in addition, supports the gage G which iixes the position o! the optical system rele-.Live to the vuil W of the cavity.

The structure of the interior of the tute T muy best oe understood by inspection of Figures 3 and 5, the former showing un axial cross section il view oi this tube and the latter a transverse cross sectional view. As wili be evident from th'. se views, an optical tube 20 is mounted in the upper portion of the inspecting tube T and is supported therein by spaced inserts 22 located et intervals along the length thereof. These inserts may he of brass or other suitable material machined t0 nt snugly within the interior of the inspecting tube T and to receive snugly the koptical tube 2O andl other elements within the inspecting tube to sustain them in position. Although a relatively small spacing between thc inserts 22 is shown in Figure 3, it will he apparent that the number ot these inserts may be varied. in accordance with the mechanical strength of thetuoes 20 and T.

The head portion H is housed in tu'oe 24 which snugly nts over the tube T and hasl o cutout portion 26 tc form a window through which passes the light necessary to illuminate the interior of a cavity being inspected. The lamp 28 is disposed immediately below this window and inthe bottom portion cfrr the tube 24. This lamp constitutes the source ci .thevultraviolet and: visible light which illuminatesthe cavity under inspection. The lamp 2E is shown in elevational` view in Figure 3 and trnnsversercross section in Figure 4. A lens 30 is tted over the lamp 28 and acts to assure uniform illumination of the interior of the cavity from the opening ery window 28. This lens may be supportedxwithln the tube 24 by any suitableV method, as for example by grooves 36aand 39o 1n end cap 32 and supporting insert 22, i espectively.

A shiteolc retractable filter :it` lsrinterposed between the lens 30 and the window. 26 to cutl ou all visible portions of the light spectrum issuing from the lamp 2B. This nlter may be supported f for sluiting movements along the axis of tube 24 by any suitable method. By way o! illustra.- tion and not by way ot limitation, this lter is shown supported 'within tubey 24 oy two parallel grooves Bil, Figure 4, cut in. ".ie interior of that tube to iit 'snugy the filter io position wolle permlt; 6 shifting movements thereof along the tube.

Shiitingor retructing movements of thev iilter 36 are contrcl'ed by the wire or' rod 'il which has adownwardly extending tip portion 40o fitting into a. suitable cg; ming on theeud oi' the ilt/er 3G. This rod este-nr.; through tire tube T and out through the end portion ci the housing 42 oi vthe operating portion O. At its end, the rod 4G is shaped to form a loop Bilo that may readily be grasped by .he operatorl to shift the filter Slik from the retracted position shown in Figure 3 to the opera-ting position shown in Fieure 6.

The lamp 2: is a high pressure mercury vapor lamp having n quartz envelope 44 containing mercury which vaporizes to torni the conducting medium through .which the are passes. Illumination having a considerable proportion o! ultra-violet light is produced by current new between the two operating eiectrodes in the opposite ends of the lamp indicated at 46, and 46, Figure 3. Electrode 4S is connected to the tube 24 and electrode 43 is connected to insulated wire which eme-nds through' theA tube T as shown in f Figure 5 and. through the housing 42 o5.' the ob serving portier O to the connector indicated atv 52. Cable 54 is attached to this connector for supply'- of electrical energy to the lamp 23 from a suitable source.

The filter 35 muy he any one ot the various filters capable o.' opposing passage of visible light :lille permitting passage ot ultraviolet light. Jhon lt is in the operating ',iosition shown in Figure 6, this filter extends completely over the window 26 and thus ents or! all visible light isto sustainthesame I suing from the lamp 2S. During this condition, the head H illuminates the interior of the cavity being inspected with ultraviolety light only since the nlter 36 intercepts all the visible components of the light produced by the lamp 2B. When the loop lila, Figure i, is pushed backwardly by sultable pressure by the operator, the filter 40 vis shifted backwardly to the retracted position shown in the view of Figure 3. This exposes a portion of the lamp 28 for direct illumination of the cavity being inspected and thus causes visible light to enter the cavity.

I have discovered that a lamp of the high pressure mercury arc type produces ample light in the visible spectrum to illuminate the interior of a cavity under inspection with the filter 38 in the position shown in Figure 3.

The energizing circuit for lamp 28 kis shown diagrammatically in Figure 7. The transformer i6. located externally to the tube T has its pri- 4mary windingl connected to terminals 58 to which a source of alternating electromotive force is also connected. One terminal of the secondary oi' transformer E is connected to conductor 50 through suitable cable 54, Figure l, and the opposite terminal of the secondary of transformer 56 is connected to the tube T by the cable 5l, thus to impress the'voltage of the secondary or transformer 56 across the lamp 28. A starting electrode E2 is disposed in the end of the lamp 2B adjacent i'o the electrode t6 and is Vconnected through resistance 60 to the electrode. 48 toV Ainitiate the discharge in lamp 28.

It .is the function of tube B2 to conduct cooling gases to the lamp 28. To this end the tube 82 1 extends the length of tube T and into the housing l2 of the observingl portion O. This tube opens into channel 64 in housing 42, which channel passes through the connector portion 66 of housing 62. to which the hose 68 is attached. As indicated in Figure 3, the tube 62 passes through the insert 3i and opens just beyond this insert. thus causing the gases passed through the tube to circulate about the lamp 28. As shown in Figure 2. the end 32 of lthe head Ii is provided with a plurality of holes 32a through which the heated or spent gases flow after passing about tube lamp 2li.

The gases passed through the tube'll not only provide a supply of cooling medium to maintain the lamp 28 at the temperature range moet suitable for effective operation but in addition they prevent generation of deteriorating ozone gas by that lamp. To achieve this end, these gases are of some inert gas such as. for example. nitrogen.

which does not contain oxygen and does not react to the ultraviolet radiations. Thus the interior of the head H is .not exposed to the corrosive action of ozone that would otherwise be produced and the repair and maintenance of the unit is correspondingly simplified.

The tube 2A which forms a housing for the head assembly H may be removed from the -rcmainder of the mechanism for repair or replacement. By way of example and noi'. by way of limitation, the tube 2li may be secured to tube T by a set Screw 24a.

The viewing mechanism of the present invention includes the auxiliary tube 2li which is sustained within main or inspecting tube T and which opens into prism 'i0 at one end and the eyepiece 'l2 at the other end. It is the function of prism to deflect the light rays from the mner surface of the cavity uncer inspection and to cause them to pass down the tube where the first lens '16a acts to produce un image in tube ilu in a plane normal in the axis thereof. To this end, this prisni is supported byinsert 'M whichk fits snugly in the enfi of thc tube 2li and holds it against the upper portion thereof which is out off to fit the contour ofthe prism.v The prism 10 may be seen in end view in Figure 5.

As shown in the view of Figure 8, a plurality oi spaced lenses 'I6 are disposed at intervals along the length of auxiliary tube 20. These lenses are preicrablyof the achromatic type and may be spaced every four inches. thus using a total of 13 lenses in a five foot tube.

The disposition of lenses 'i6 at frequent intervals along the length of the tube 20 prevents loss or distortion of the image when the tubes T and. 20 rirev inadvertently flexed eitherk by their own weight or 'by the manner in which theyare handled. It is desirable to construct these-tubes cf small diameter to fit into small openings to reach relatively inaccessible cavities. As a. consequence of these smalldiameters, these'tubes are relatively fiexble and flex under their own weight to a degree suicient to obstruct-direct vice.r of an image formed near the prism end-of tube 2li. Each lens 1E acts to produce an image on one side. corresponding to the image located on the otherside, and since the axis of eachlens is shifted as the tube 20 ilexes, the` positions of these images likewisel shift to produce the image at the eyepiece l2 even though direct view through the tube 2U is not possible. Thus each successive lens pickslup the image of the interior of the cavity on one side and forms a like image on the opposite side. v

The' eyepiece 12 includes lenses suitable for viewing the image produced by the lenses T6 immediately adjacent this eyepiece. Any one of several mechanisms well known in the art may be used for this purpose. Preferably. though not necessarily, this` eyepiece may contain'an ocular lens system capableof magnifying the image produced by the lens 7G immediately adjacent the eyepiece, thus to permit visual inspection of the image' with maximum detail.

It is the function of the gage G. Figure 1, to fix the distance bei-Ween the head H and the inner wall W ofthe cavity being inspected at the distance necessary to produce a sharply focused image. Since wide-angle, short focaleistance lens elements are desirable to achieve a maximum area of inspection, this focusing is relatively critical-and it is difficult and even impossible to achieve the desired focusing by merely inserting the lengthy tube T in the cavity. The gage G provides a mechanism whereby the operator can nx the distance to the wall of the cavity at the proper value and thereby assure clear sharply focused images.

The gage G comprises an arm 89 which is pivotally supported from the upstanding bracket 82 by the pin Bil. The bracketl 82 is fixed to the upper portion of the tube T. The remote end Bia. of the arm 8i) is rounded oil to slide easily against the wall W of the cavity being inspected and permit the arm readily to rotate about pin 8l:

without any tendency to catch when the instrument is inserted or removed from the cavity.

The crm lill is biased to a predetermined position relative to the tube T to cause the end 88a to reach the seleftecl` distance from the head H to provide sharp focusing of the image. Adjustable mechanism is provided to alter the position to which the arm :lll is biased to accommodate different opticai system components. By way 0l.

7 example, this mechanism may include a housing Il in which rides a plunger 88 having a bifurcated. end portion 8M to receive the arm 90 andthe pin 92 which pivotally supports that arm in the Y plunger 88. At its opposite end, arm 9D is received-in a similar biturcated end portion sib of the arm 80 and is pivotally supported therein by the pin 92.

The plunger 88 is provided with an end flange 88a upon which one end of spring 961s bottomed as will be evident from the broken away portion oi the view of Figure 9. The opposite end el the spring 9G is bottomed on the inwardly extending ilange portion 86h oi the housing 8S as also indicated in the broken away cross sectioned portion of the view of Figure 9. Thus spring 8B normally holdsy the end flan-ge 83:: o: plunger B8 against the wall 861i oi housing 88 and lli t the arm B a predetermined angle relative to the i axis of tube T. thus causing the. end 80a of the arm 80 to extend the desired distance from the head H. When the arm Btl rests against the wall W of the cavity being inspected, the operator is assured that the head H isin position for proper focusing of the image. He can determine that this fact exists by the force transmitted to the end ot tube 'l when the arm 8b rests against the wall oi' the cs vity.

Adjustment ci the distance arm 80 extends from the axis oi the tube T may be achieved by mounting the housing 86 to ride in a suitable track on the suriace ci' the tube T. This track is indicated at 98, Figure 10, and has oppositely disposed. walls 88a and 93h between which the housing 86 rides. Anadjustable assembly |00 likewise rides in. this track and is attached to the housing 85 by the arm I D2. This arm supportsthe turnbuckle screw itil whio'il has shoes |06 threadedly secured to its opposite ends to engage the walls of the track 98. An arm `lll is fixed to tuznbucklc screw (Ud to permit rotation thereof selectively to' engage or disengage the shoes |06 against the walls of the track 9E, thereby permitting adjustment of the position of housing 86 and her-.ce the distance between the housing H and the wall of the cavity when the arm 80 engages that wall.

In addition ro providing a method oi accurately iixing the distance from the head H to the wall W, the arm 3D of gage G bears a uorescent marker which is visible to the inspector at all times. This marker is in the form. of a hair line, as shown at 8|, Figure lA is made of some suitable material which fluoresces upon application of ultraviolet iight. By providing this reference hair line at a point in the iield of vision, it is always possible for the inspector oi the instrument to identify a known portion of the field oi vision and to concentrate his attention thereon. Moreover, he is always advised thatthe ultraviolet light source is in good operating condition and can act with assurance that he will observe the presence of any fluorescent material in the wall W. Thus the possibility o.' the light source going out or becoming ineffective. together with the possibility oi' the inspector failing to view in the right portion of the rptical system to see the wall. is avoided.

'I'he appa ratus of the resent invention is particularly adapted to the inspection of cavities by methods srci as that disclosed in Robert C. Switzcr Pateizt 2,259,400. In accordance with this method. the article to be inspected is immersed n or painted with a penetrant liquid containing fluorescent substance capable ot glowing under ultraviolet illumination.

Alter application of this liquid to the surface to be inspected, the liquid is supercially removed by wiping or drying. leaving only deposits of the liquid and uorescent substance in the cracks or aws in the surface. When ultraviolet illumimttion is applied to the surface by the apparatus of the present invention. the iiuorescentmaterlal radiates visible light and the presencev of cracks detected by obsel. ving the image through the eyepiece l2. Weld bums and similar normally visit-le imperfections in the walls ot the cavity are, of course,-detected by shiltlng filter 36 to the retracted position.

While I have showna particular embodiment of my invention, itwill of course be understood that I do not wish to be limited thereto since many modiilcatiorni bothin the elements employed and their cooperative structure may .be made withc'xt departing fromy the spirit and scope ci my invention. 1, oi course, contemplato by the appended claims tocovcr all such modiicatlons and alternative constructions as fall within `the true spirit and scope ci my invention.

I claim es follows:

l. Aninstrument for inspecting theinterior o! a cavity illuminated with invisible light including in combination. a head for insertion in said cavity. a source oi ultraviolet light within saidhead. viewing elements mounted in'said head and oper able to produce an image oi the interior of said cavity through fluorescence oi said cavity by theaction of said ultraviolet light, and a. member mounted in spaced relationship from said head and in the eld ci view of said elements, said member having a mark thereon of material capable of converting saidinvisible light to visible light to identify a predetermined point in said image.

2. An instrument for inspecting the interior o! a cavity illuminatedv with. invisible light including in combinatiorua lengthytube to be inserted in said cavity, said tube having a window 'te-permit passage of light from-:said ca 'ity to the interior oi said tube. a source ofy ultraviolet light within said window. optical elements to'produce an image of said cavity as seenI from said window, viewing elements located at the remote lend of said :tube to permit viewing said image to inspect the interior of said cavity. and a member extending from said tube totheleld oi vision oi' said element and bearing a marking of=.material capable-oi converting said invisible light to visible light t0 form a reference point on saidA image.

3. A device for' illuminating the interior o1' a cavity comprning in combination, a lengthy tube having a head portion at one end, a source o! both visible and invisible light disposed in head portion sain head portion having. a window to illuminate said cavity .when said lamp is operating, a iilter ea'. able oi' transmitting onlysaid invisible light slidabiy supported relative to saidwindow to cover or uncover said window, and a 1 rod in engagement with one end with said iilter and extending the length o! said tube to slide said iilter and selectively interpese said iilter over said window.

4. An insarument for illuminating .the interior o! a cavity with ultraviolet light, said instrument comprising a lengthy tube, a source of ultraviolet light disposed near one end oi said tube, a pipe in said tube opening at a point in proximity to said source and extending toward the opposite end otsaid tube. and asouxce o! oxygen-free inert gasrv underl pressure exceeding the pressure about said ilrstv source connected to said pipe to 9 cause a stream of inert gas to pass about said source and prevent production of corrosive gases.

5. An instwrnent for inspecting the interior of a cavity including in combination a lengthy tube having one end to be inserted in said cavity, said tube having a window near said eno', a mercury vapor lamp disposed in. said tube near saidsource to illuminaie the interior of said cavity, an electrical conductor extending from said lamp to the other end of said tube for connection with a source of electrical energy for said lamp, a illier capable of transmitting onb' untraviolet light shittably disposed in said tube to cover said window, a rod attached ai'.l one end to. said iilterand extending through said tube said other end thereof to permit shifiing said lter to expose said cavity to direct illumination from said lamp, an auxiliary tube within said ilrst tube and opening in proximity to said lamp, a sourceof nitrogen connected to said auxiliary tube to cause. cooling gas flow about said lamp, a second auxiliary tube opening near the end of said window. optical elements to produce in said secondA tube an image of said cavity as seen from said window, lenses disposed in said last tube at spaced intervals to transmit said image to the end thereof, `and anar-m pivoially supported from sai-:l end oi said tube and yield ably biased to aposition where its remote-end is spaced from said tube by the distance from said tube at which an image oi' the interior oi' said cavity is sharply focused", said arm having a fiuorescent marking to form a reference point on the viewing system.

6. In an instrument for illuminating the walls of a cavity having irregularities 'thereof coated with a fluorescent sabstancsga lengthy tube portion arranged for insertion within said cavity, means for spacing the head o!- said tube a predetermined distance from the walls of said cavity, the head of said tube havinga window therein, a source of light mitt'mg both visible and ultraviolet rays disposed within said head in registry with seidl window to illuminate ysaid cavity. e. illter capable of transmitting only ultra-violet light arranged for sliding movementacross said window, and operating means along said tube for selectively moving said ilter across said window.

7. In an instrument for` illuminating the walls of a cavity having irregularities thereof coated with e. .fluorescent substance, a lengthy exible tube arranged for insertion within said cavity. said tube having a window therein, a source ci' light. emitting both visible and ultra-violet 11h25. disposed in proximity to one end of tl: tube in registry with said Awindow to illuminate selected portions of said cavity, a filter capable of transmitting only ultra-violet iight disposed in sliding engagement across said window, operating means extending along said tube for moving said lber across said window, and a plurality of lenses mounted in said tube at spaced inten'als, each of said lenses being arrangedy to pick up the image from the next preceding lens and forman image for the next succeeding lens. and viewing ele.- ments to observe the image produced at the last of said lenses.

HENRY G. BOGAR'I..

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mamon :ATIm'rs 40 Number Country Datz'.

267,818 Germany 1 Nov. 29,1913 419,121 Great Britain Nov. 6, 1934 509,308 Great lritain July 11, 1939 685,065 France Mar.. 25, 1930 w O'IHER REFERENCES Feldman article in Am. Jour. ci? Ophthalmology. vol. 25, Nov. 194-2; pp. 1357-1361'. 

